1. Field of Invention
The invention relates to a light source, and more particularly, to a back light module.
2. Description of Related Art
With the rapid advancement of flat display technique, the current liquid crystal displays are widely used in daily life. The liquid crystal displays have the advantages of light weight, compact size, low power consumption, and smaller thickness, so that the liquid crystal displays are progressively replacing the conventional cathode ray tubes (CRT).
The liquid crystal display has a liquid crystal panel and a backlight module, and the backlight module is configured on the back side of the liquid crystal panel for providing the planar light to the liquid crystal panel. According to the positions of the light emitting devices, the backlight modules may be classified into a direct type backlight module and a side type backlight module. The side type backlight module uses the light guide plate to guide the light emitted by the light emitting devices configured at one side of the light guide plate and to provide the planar light to the liquid crystal panel. Furthermore, according to the types of the light emitting devices, the light emitting devices could be also classified into a light emitting diode (LED) backlight module and a cold cathode fluorescent lamp (CCFL) backlight module.
In the side type backlight module using the light emitting diode as the light emitting device, a plurality of light emitting diodes which are arranged in a straight line and spaced apart from one another are configured next to the light incident surface of one side of the light guide plate. Theses light emitting diodes respectively emit a plurality of light beams and the light beams enter the light guide plate through the light incident surface of the light guide plate. Because the directivity of the light emitting diodes is higher (i.e., a limited light emitting angle range), bright regions are formed in the light guide plate within the light emitting angle range and close to the light emitting diodes, and dark regions are formed in the light guide plate outside of the light emitting angle range. The light guide plate may not be able to provide a uniform planar light source due to the existence of these bright and dark regions, and this is referred to as the “hot spot” phenomenon. It should be noticed that with the increasing of the power of each of the light emitting diodes, the number of the light emitting diodes configured at a side of the light incident surface of the light guide plate could be decreased. However, when the number of the light emitting diodes is decreased, the distance between two adjacent light emitting diodes is increased. Thus, the area of the dark region is increased and the hot spot phenomenon is getting more serious. Hence, the uniformity of the planar light source is getting worse.
Besides, FIG. 4B of Taiwan patent No. M316410 discloses a light guide plate with light sources arranged to be corresponding to one or more corners of the light guide plate. There is an indentation with the flat surface or the curve surface at the corner position. United States Patent Publication No. 20070177405 discloses a light guide plate having two light incident corners, wherein light sources are disposed at the two light incident corners. FIG. 3 of Taiwan patent No. 589491 and U.S. Pat. No. 6,913,366 disclose a light guide plate having two corner-less surfaces, wherein the first light source portion has two light emitting sources and these light emitting sources are arranged to be corresponding to the two corner-less surfaces of the light guide plate. Taiwan patent publication No. 200700797 discloses a light absorbing material which is disposed in the light path and close to the light source. The light absorbing material could be coated on or attached to one surface of the light guide plate or one surface of the optical film.
Taiwan patent No. M318136 discloses a reflecting plate having a surface with the scattering points thereon, wherein the shape of the scattering point may be a geometric figure such as a round, a rhombus, a triangle, an ellipse or a taper. The areas of the scattering points vary gradiently. The scattering points are separated from each other with a fixed distance or with a distance varying gradiently. Moreover, the scattering points are tightly arranged at the four corners of the reflecting surface.
Taiwan patent No. I298410 discloses a backlight module including a back plate and a light source. The light source is disposed at two adjacent corners of the back plate. The backlight module further includes a dissipation part, wherein the dissipation part is disposed between the light source and the back plate. Taiwan patent No. M274546 discloses a planar light source apparatus including a frame, a reflecting plate, a light guide plate, a light source, and an optical film. The frame has a plurality of hollow portions to accommodate the reflecting plate, the light guide plate, the light source, and the optical film.